Separation of Mixtures (Distillation, Chromatography, etc.) MCQs

Q1. A coastal salt farmer floods shallow pans with sea water and waits for the sun to dry them out, leaving white crystals behind. Which separation technique is he chiefly relying on?

• A.Evaporation
• B.Filtration
• C.Distillation
• D.Sublimation

Answer: A. Evaporation

The dissolved salt cannot be filtered. Letting the solvent (water) escape as vapour by the sun's heat and leaving the solute (salt) behind is evaporation. Distillation is ruled out because the water vapour is not condensed back.

Q2. A laboratory worker needs to recover pure copper sulphate crystals from its aqueous solution while leaving behind the soluble impurities, so that the crystals are well formed and pure. Which method should be chosen?

• A.Crystallisation
• B.Filtration
• C.Simple evaporation
• D.Sublimation

Answer: A. Crystallisation

Crystallisation slowly cools a hot saturated solution so that the desired solute forms pure crystals while soluble impurities stay in the mother liquor. It is preferred over evaporation to dryness because evaporation traps impurities and decomposes some salts.

Q3. A chemistry teacher wants to obtain pure water from a sample of ordinary ink, which is a dye dissolved in water, in a single run. Which technique recovers the water as a clear liquid?

• A.Distillation
• B.Decantation
• C.Chromatography
• D.Filtration

Answer: A. Distillation

Ink is a solution of a non-volatile dye in volatile water. On heating, the water boils off, is condensed in the condenser and collected as pure distillate, while the dye remains in the flask. This is simple distillation.